The electrolytes most commonly used in electrolytic cells are liquids in the form of solutions containing ionic species, which allow migration of ions between the electrodes of the cell. The electrolytes used suffer from several disadvantages in that they are often corrosive and toxic and present handling and storage difficulties through spillage or leakage from the cell.
In order to overcome the disadvantages inherent in liquid electrolytes and to obtain superior long-term storage stability there is interest in solid polymeric electrolytes in which ion mobility is achieved through coordination by sites on the polymer chain of electrolyte ions thus promoting electrolyte dissolution and salt dissociation. One polymer which has been examined extensively for this application is poly (ethylene oxide), which is able to form stable complexes with a number of salts. However, the electrical and mechanical properties of such electrolytes require further improvements before application is appropriate, especially for cells required to operate at or near ambient temperature. A major problem with poly (ethylene oxide) electrolytes at temperatures below 60.degree. C. is their high crystallinity and the associated low ion mobility.
Recent advances in the field of polymeric electrolytes have been based on the modification of the polymeric structure in order to increase ion mobility and maintain a high value of such over a wider temperature range.
Routes to achieve this have been disclosed in UK Patent Applications 8421193 and 8421194 and in UK Patent Application 8520902, claiming priority from the earlier applications. The routes involve the use of for example, an oxyalkane coordinating unit in the form of an oligomeric sequence such as poly (ethylene glycol) linked by flexible groups at --OH termini to form both linear or cross-linked polymers, so that crystalline, non-conducting phases are essentially eliminated. The physical form of the electrolyte prepared can be controlled by the nature of the constituent parts of the resultant electrolyte and the degree and nature of any cross-linking.